Bent tube section and a method of



June 2, 1942. n. s. HARDEk 2 5, BENT TUBE SECTIONS A METHOD OF PRODUCING THE SAME Filed Nov'. 8, 1938 2 Sheets-She et J.

INVENTOR.

Delmar 5. H0 rater YMM. WQM

ATTORNEYS I June 1942- D.- s. HARDER 75 BENT TUBE SECTIONS AND A METHOD OF PRODUCING THE SAME Filed Nov. 8, 1933 2 Sheets-Sheet 2 INVENTOR.

Delmar 6. Harder ATTORNEYj Patented June, 2, 31942 UNITED STATES.

Q BENT TUBE SECTION AND A METHOD OF PRODUCING THE SAME Delmar S. Harder, Detroit, Mich, assignor to General Motors Corporation, Detroit, Micln, a corporation of Delaware Application November 8, 1938, Serial No. 239,524

4 Claims. (Cl. 153-2) I This invention relates to bending of tubing and more particularly to a method of bending a tube and the bent tube as an article.

When a tube is -bent about a sharp corner, for example; a 90 bend, the tube buckles and has its cross-section substantially changed and materially weakened at the bend. It is an object of this invention to bendtubing about sharp corners and retain substantially the original strength'of the tubing at the bend. This object is achieved by predetermining and controlling the cross-sectional shape of the tube 'at the bend. i

In the drawings:

Fig. 1 disclosesa typical application for sharp cornered structural tubing-a supporting frame for automobile seats.

Fig. 2 shows the machine for bending, with a tube in position to be bent.

Fig. 3 illustrates the details of the jig arm at the section 33'of Fig. 2.

1 Fig. 4 is a cut-away 'view of the dies of the bending machine at the end of the bending stroke, revealing the relation of the work and the di s.

Fig. 5 is the section 5- -5 of Fig. 4 showing the relative. positionsof the dies and materials. at that point upon the completion of the bending stroke. v

Fig. 6 is a section at B6 on Fig. 4.

Fig. '7 is a section through the dies and the work during the bending stroke. v

Fig, 8 illustrates the work and dies at the completion of the stroke. A i

Fig. 9 is a perspective of the lower die.

Fig.1!) is a side view of the finished product.

Fig. 11 isthe section of Fig. 10 showing thestructure at the bend. 1

Figs. 11a and 11b are-sections along the lines ||a-'|.|a and Hb-Hb of Fig. 10.

Figs. 12 and 13 are sections through the cor- 4 ner of the bent tube which has previously been reinforced by a tube and strip of metal respectively. 1

In Fig. 2, I2 generally denotes an upper die holder and I3 a lower die holder. A guide post l1 keeps them in alignment. The tube to be bent, referenced H. when placed on male die member I8, is held thereon by the jig arms l5 and I6 (Fig. 3) which are rigidly attached to the lower. die iii. The ends of the jig arms l5 and I6 take the form of sockets 40 which abut the ends of the tube to hold it against longitudinal movement and which fit over the top and side portions .of the end of the tube to hold it on the die I8 against lateral movement Female diemember 2| is in the form of an inverted V socket and complements die member l8 in bending the tubing l4.

Die member 2| is a composite die comprising upper die member 43 andfront die member 23. Die member 2| is held to the upper die holder |2by a bolt 22. Die member 23 is secured to the upper die holder l2 by bolts 24 and pin 25.

The'lower inner edge of die member 23 is bev- 10 eled to facilitate the sliding of the work M and die member I8 past this. point. The die member I8 is backed by the die member 26 and both are secured to the lower die holder I3 by bolts 21.

The contour of die members it and 2| will depend upon the bend desired. As herein shown' the tube- I4 is bent about a 90 angle. Therefore the lower die member i8 is an inverted V in form. The sides of die l8'are grooved at 28 to fit the tube. The complementary die member 2| is similarly grooved at l9, Fig. 5. The side die members 23 and 26 form vertical plane walls awhich restrain lateral distortion of the tube. 1 The die member 18 has a rounded head portion in the form of a bead 30 of such shapeas to form the indentation 30a in work M, Fig. 10,

and of cross-section such as to form the rounded portion 30b of Fig. 11. Die member i8 is provided with shoulders 3| on each side of the bead v30. These shoulders 3| project above and without the projected plane of grooveddie faces 28. Thus, as viewed in Fig. 10, the radial diameter of the tube taken along the radius of the bend or height of the tube at the bend, as viewed in Fig. 11, is decreased but the width of the tube at the bend, as viewed in Fig. 11, is the same as the original diameter of the tube. This shortening of the radial diameter or height, of the tube at the bend provides sufficient metal so that the side walls as (Fig. 11) of the tube can be straightened or pressed into plane form without decrees-y ing the thickness of the wall of the tube at the bend.

If for any reason it is desired to increase the strength of the tube at this corner bend, this can 4 be done in several ways. A second tube, either splitor seamless, that fits snugly inside the principal tube M can be inserted at the place to be bent. The result will be adouble wall bend instead of a single one, see Fig. 12. Another way to reinforce the corner is to place strip metal within the tube at the area to be bent. Preferably the metal strip is as wide as the inside diameter of the tube and is firmly gripped by the sides and thus acts as a strengthening member, see Fig. 13. i

' v ably guidedinopening 42 in die holder I2.

01' the line u-n.

- After the tube has been positioned on die memher l8 and its ends interengaged with the sockets 40, theIdie members I8 and 2| are brought together. As the die members are brought togeth- J er they are guided by posts I! and 20 and their cooperating guide openings 4| and 42 respectively. Post I! is fixedtodie holder l2 and slidably guided in opening 4! in die holder l3. Post member 20 is fixed in die member l3 and slid- Preferably the' upper die 2| descends on the stationary bottomdie l8, see Figs. 7 and 8. As the dies close, the bead 30 of die member l8 preferably first indents the tube l4 as at 30a and 30b and thereafter further closing of the dies causes die -2l to bend tube I4 about die l8. ,However, the

step of indenting and bending can be simultaneousr Fig. 4 shows the die members [8 and H at the end of their working stroke with the tube 14 between them. In the closing movement. of

the dies, die 2| bends the tube 14 about die 68 causing the ends of the tube to disengage socket 40 in the jig arms l and Hi.

As the dies complete their stroke the side walls 33 of the tube at the corner are flattened into plane surfaces against die members 23 and 26 and the outer face 34 of the bend is also flattened along the outer circumference of the bend byfdie 43. Rounded corners are also pro- ,duced between the side faces 33 and the outer face 34 at the bend. The inner face of the tube at the bend .is indebted as at 30b with an indentation having a semicircular' cross-section which adds considerable strength t0 the tube at the bend.

, As shown in Fig. '11 the cross-section of the,

tube at the bend may be described as a channel section havingvan outer wall 34 and side walls 33 which are bridged by the wall 30b which curves inwardly of the channel. The indentation 30 is deepest along the line l|-ll of Fig. -10 and then becomes shallower and gradually fades out and merges with the tube on each side The flattened outer circumference 34 reaches its greatest width at line |l -ll, Fig. 10, and it too gradually decreases to flatten the side walls and the outer wall of cross sectional form of the tube is substantially maintained. However, bend 46 is about a radius of insufficient length to maintain the original cross sectional shape of the tube. It is evident that the herein described method of bending a tube is particularly applicable to sharp bends, that is, a bend of such short radius that the original cross sectional shape of the tube cannot be maintained during and at the completion of the bend. The method hereindisclosed is essentially characterized in that the change in'cross sectional shape of the tube at the bend is ,con-

trolled so that the tube at the bend is changed from a, tubular section into a section having substantially equal strength.

I claim:

1. A method for bending a tube comprising indenting the tube in the area to be bentand bending the tubeabout a sharp corner so that the indentation is on the inside of the bend and during such bending confining the tube and pressing the same to flatten the side walls and the'outer wall of the tube at the bend.

2. A method of bending a straight length of which comprises longitudinally indenting the face of the tube that is to be the inside of the bend, bending the tube at the indentation by applying force substantially perpendicular to the tube at each side of the said corner so that said indentation is on the inside of the bend and fiattening the tube on the outer face of the bend and on the sides of the bend perpendicular to said flattened outer face while said tubing still engages said corner.

4. An article of manufacture comprising a tube having a substantially right angle bend, an outer face at the area of the bend which has its greatest width at the mid portion of the bend and decreases in width and gradually merges into the round well of the tube on each side of the mid portion of the bend, the side walls of the bend being substantially flat and merging at each end into the round side walls of the tube, the inner face of the bend being curved inwardly of the tube-to a depth which is greatest at the mid portion of the bend and which gradually decreases on either-side of the mid portion of the bend.

DELMAR S. HARDER. 

